Tonepad's Maestro FSH-1 has a strong ticking

Started by gigimarga, July 28, 2008, 03:40:12 PM

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Ripthorn

The strange thing is I have mine working in S&H mode, but filter seemingly does nothing.  I did have to substitute the resonance pot with a 1M because I couldn't get a 2M.  I also have a strong ticking.  A 10 uF electrolytic helped some, but still noticeable.  I am going to try a TL022 or similar to see if that helps.  I wonder if maybe the switch thing could activate a diode so that the LFO can't send out anything when in filter mode.  Have the cathode oriented towards the LFO so that it blocks the LFO signal when in filter mode, hmm.  I just might have to try it when I get some time.  S&H mode sounds great, though.  Strange, seems most have a problem with S&H and not filter  mode.
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boblob

Just want to chip in... I had this up on the breadboard using TL022s (good choice as they have a very low current draw). Initially pretty noticable LFO tick. Removed decoupling caps from the +ve side of the supply, leaving just the two 220uF caps on the -ve side of the supply. No ticking.

Also worth trying bigger caps for the 150nF off the collector of Q3 - this should help damp some of the feedthrough from the LFO. The Gristleizer has a similar thing - a pair of low-pass filters designed to take the edge off the LFO tick.

Atodovax

Quote from: flo on August 02, 2008, 08:22:46 AM
Hi, if the problem is due to LFO ticking "bleeding through" to the audio path, there are several things that you can do.
I found the following tips on this site when I was looking to cure LFO ticking in an UltraFlanger. The following tips were written by various people (Mark Hammer and others) and were used to address deticking LFO's in general but I'll try to rewrite it to make it appropriate for deticking the FSH LFO:

http://www.diystompboxes.com/smfforum/index.php?topic=61250.msg480708#msg480708

There are a few separate matters to be addressed (quotes from others slightly rewritten to adress the FSH LFO):

The LFO and audio path need to be decoupled from each other.  You should run something like a 100R resistor from the shared +9v source to the V+ pin of the LFO opamp chips (especially IC5 which generates the LFO), and run a 10-100uf cap to ground from that pin.  This will give each chip a small reservoir of current to hold them over in case one of the other chips makes a sudden demand for current.  Those sudden demands are what you hear as ticking.
The FSH is using a 741 opamp for the LFO path (IC5) and 3080 OTA's for the (filter) audio path (IC1 IC2 Q1 Q2).  This will let you decouple them separately, instead of having whatever the LFO does impact directly on the OTA's in the same hunk of epoxy.

It is also a smart idea to use a low-current op-amp for the LFO.  Why?  Because the "standard" opamp LFO produces a square wave.  What you hear as ticking is the sudden current draw as the square wave rises, placing noise on the power line.  The decoupling reduces the extent to which that spike "bleeds" into other parts of the overall circuit.  Using a low-current op-amp reduces the magnitude of that spike in the first place.  Think of the decoupling as being like ear muffs, and the low-current op-amp as being like smaller speakers.  Use of either will keep the volume of undesirable sounds down, but use of both will reduce it even further.
You will note in glancing through schematics of commercial phaser, flanger, chorus, and tremolo pedals that many of them will use either an LM358 or a TL022 dual op-amp for the LFO, and use different op-amps elsewhere in the audio path.  They use those particular op-amps because they draw less current.  There are other functional equivalents, I'm sure.  I just wanted to explain why you often see those ones.

Another strategy for deticking involves a slight change to the LFO design itself.  Nicholas Boscorelli explains this nicely in one of his Stompboxology ( http://moosapotamus.net/IDEAS/stompboxology/stompboxology.html ) newsletters, and you can sometimes see this in commercial designs.  The gist is to change that initial square wave into what is more or less a trapezoidal wave.  What we hear as ticking depends on the suddenness of the rise-time.  If the rise-time can be slowed down even just a wee bit, the current draw of the LFO is essentially distributed over a long enough period of time (in electronic, not human, terms) that it does not produce disturbances elsewhere in the circuit.
So, reduce the amount of current required to produce a square wave, make the rise-time of the square wave less sudden, and isolate the chip requiring the sudden current draw from the rest of the circuit.  That's how you get a tick-free modulation pedal.
"In my Small Stone (russian) I have a 1uF capacitor between + and - input of the comparator opamp which is the one that produces the square wave of the LFO. This seems to detick the Small Stone, probably, by reducing the rise time of the square wave."

I solved the ticking by grounding leg 3 of speed to ground when bypassed but i experience a strong pop when i engagge the effect. Any ideas?